Paper-covered gypsum board



P 1957 R. s. VON HAZMBURG 2,806,811

PAPER-COVERED GYPSUM BOARD Filed Dec. 31, 1954 INVENTOR.

United States atent Dfihce PAPER-COVERED GYPSUM Basal).

Romulus S. von Hamburg, Wilmette, 111., assignor to United States GypsumCompany, Glncago, 1b., a corporation of Illinois Application December 311954, Serial No. 479,190.

7 Claims. (Gl. 154-86)- The present invention relates to an improvedform of gypsum-core plaster board, in which the paper cover sheets areof such a nature that they will not split longitudinally of the board.

As is well known inthis art, paper covered gypsum boards are made byenclosing a mass of plastic watergauged gypsum composition between papersheets and allowing the resulting product to set up; whereafter itisdried and cut up into sheets of the. desired size. One of theessentialfeatures of such a board-is a firm adherence of the central gypsum coreto the cover sheets, so that the board will not delaminate at theinterfacebetween the core and the cover sheets.

This has been quite satisfactorily accomplished in the past by theadditionof'farinaceous materials'tothe core. These farinaceous materialscontain a certain percentage of a water-soluble starch which, during thedrying of the gypsum board, will migrate to the interface between thecore and the cover sheets, and will hence be closely associated with thegypsum crystals which interlock with the fibers of the cover sheets,thereby preventing their release. Thepresence of the starchy orfarinaceousmaterial also serves to protect the fine gypsum crystals,from becoming calcined during the drying of the board, forv if they didso, they would lose their strength, with resulting destruction ofthebondbetween the, core and the cover sheets. When such loosening of thebondoccurs, the resulting boards are known as peelersfi The gypsum core isthusexposed, and the board, at least to the de. gree that the peelingextends into the board, isrendered useless, and must be trimmed down toobtain pieces of board of'a useful size.

It has now been discovered that another type of defect can make itsappearance, and lead to defective boards of the general nature of.peelers, except that in the present case the delamination occurs not atthe interface between the core and the cover sheets, but is the resultof the delamination of the cover sheets themselves, which split eitherbetween the plies of the paper, or, in some cases, involve actualinternal splitting of the plies themselves.

The cover sheets usually employed in the production of gypsum coreboards consists, in the case of wallboard which is intended to form theinternal walls of rooms, of two types. The outer cover sheet is in theform of a paper built up of: a plurality of plies, the two outer pliesbeing usually of a somewhat better grade of paper, such as manila paper,the furnish for which is made of a mix ture of ground-wood and sulfitepulps. The inner plies, including the one which will be in contact withthe gypsum core of the'board, is usually made of repulped newsprint,either used papers or over-issue newspapers. The paper used to line therear side of the board is usually made of a plurality of plies of suchrepulped newsprint. In any event, the papers are made on what is knownas a cylinder machine, the pulp being picked up on rotating screens, sothat a plurality of layers or plies will be ob tained, which, by beingsuperimposed upon each other 21 immediately after their formation willbond to eachother and produce a. substantially uniform piece of paper.Under certain circumstances, such paper is subject to separation of theplies from each other, i. e. it may delaminate.

When gypsumboard covered with such a laminated or multiple-ply paper is.dried, there appears to be set up in the paper. rather severe strains,which arebelieved to be the cause of the delamination or, in severecases, even the longitudinal actual-splitting of the ply which is near.-est. to the core. This. may occur on either the front or the back of,thegypsum board, and is probably attributable to the development ofundue strain in the plies. of the paper during the drying of the board.

It is therefore one of the objects. of the presentinvention to.provide asuitable paper cover sheet for gypsum covered wallboards which is ofsuch a nature that; it will neither. delaminate between the plies norpermit splitting off the plydirectly adjacent the core.

This object is attained by the incorporation with the furnish. fromwhich at least the innermost ply of the paper ismade of certainstrength-imparting resinous additions, which. give them. such plies, andto some extent impartto the next adjacent plies a greater degree of wetstrength, so that the plies adjacent the core will neither delaminatenorsplit, whereby all difiicultiesfrom peelers of, this specific typeare avoided.

To provide a more clear explanation. of. the application of theseconcepts to the preferred embodiment of thepresent invention, anillustration hasbeenannexed to formapart of this disclosure.

Inthedrawings:

Fig. 1 is a partial expanded view of an end of a gypsum board,while.Fig. 2. is, anenlarged diagrammatic view on a somewhat larger scale,showing a split ply which will illustrate the type of commonly occurringdifficulty inthe manufacture of-gypsum board.

As indicated hereinabove, a gypsumboard comprises a core 10 encased in afibrous envelope consisting of a manila sheet 12 and a newsprint sheet20. Normally, and depending on the characteristics desired in thefinished, board, the sheets will consist of a plurality of plies orlayers which are formed on a conventional multicylinder, paper-makingmachine. Themanila sheet-may haye, for. instance, two plies 13 and 14.made from a furnish containing ground wood and. sulfite or any othertype of suitable pulp, while plies 15, 16, 17, 18 and 19 known also asfiller plies, contain a mixture of waste paper pulps. The furnish foreach of theseplies is properly sized with conventional resin and alum,placed-into the vat, formed into a ply and then assembled into alaminated sheet. by means of the multi-cylinder paper forming machine.The assembled sheet is passed through one or more calender stacks, driedand compressed into the sheet to be used as a component of gypsumwallboard.

Theother side of the core 10 is also covered with a fibrous sheet. 20,of a somewhat different composition of furnish, since it is notnecessary that the appearance of the; back side of the wallboard need-beasrpleasing as the face side thereof. The back sheet 20 is generallyknown. as a newsliner or back liner and it likewise is made of arnumberof plies. Plies or fillers 21, 22, 23, 24,, 25-.and. 26 generallyconsist of a furnish containing a mixture, of waste papers. Ply 27normally is made from, a, furnish containing percent over-issuenewsprint. All furnishes prior to f rmation in paperare sized with. theproper amounts of rosin and alum to attain the, desired degree ofwaterproofness in the;product.

The cover sheets 12 and 20 are used to enclose-acore 10 containing acementitious slurry of calcium sulfate hemi-hydrate, water, starch,foam, set-accelerating reagents, fibers, etc. The process of makinggypsum wall- 'melamine-aldehyde product.

board has been the subject matter of many patents and is not claimedherein except as related to the application of the fundamentalprinciples of this invention.

The formed board .is produced in one continuous stream; After thecementitious core reaches a satisfactory degree of hardness the streamis cut into desired lengths, which are then passed through a drying kilnto remove the excess of Water, which was needed to render the massplastic and fiowable before its encasement. The wet board in the courseof its drying passes through a high temperature zone of about 500 F.,then through an intermediate zone of about 275 F. and finally throughdry end zone of about l50-200 F. Normally under conditions enumeratedabove, a gypsum board inch thick will take about forty-five minutes topass through the drying kiln zones and emerge as a dry sheet ready forpackaging and storage.

.In order to render. the paper sheets, of the type described above usedas cover sheets in the making of gypsum board, capable of withstandingdelaminating .or splitting within the plies, the teachings of thepresent invention is brought into play.

For thispurpose it has been found, quite unexpectedly, that the additionof small quantities of resinous materials to the paper will prevent thedelamination and splitting of the plies and that paper cover sheetscontaining such materials can be successfully used in the production ofa vastly improved gypsum board without sacrifice of production,efiiciency and loss of desirable characteristics, as well as physicalproperties, of the gypsum board;

"More surprising however was the fact that such resins need only beadded to the plies at the interface with the core to eliminate entirelythe splitting at the ends of the boards as heretofore frequentlyencountered. Obviously all of the plies could very well contain suchresins and still be within the spirit and scope of this invention asclaimed.

It has been found that the addition of such resins, in quantities aslittle as one-half percent, by weight of the paper involved in theparticular ply, is all that is needed to obtain the desired results andthat resin can be added to the fiber slurry at any stage prior to plyformation with beneficial results, provided however that there issufiicient time for its substantial and uniform dispersion among thefibers. The resin is preferably added in an emulsion form, or as asolution, either directly to the head box supplying the furnish to theindividual cylinder vat, or at some place before the Jordan as the pulpis processed through the paper making plant. Obviously it can be addedat any stage, but in case of certain plastics which react within certaintime limits, it is advisable to have the reaction take place as close aspossible to the vat or sheet forming machine.

A delamination-prevention material which has been found particularlyeffective is a melamine-aldehyde con densation supplied in dry form andsold under a tradename of Parez-607. As mentioned previously, onehalfpercent of such a resin based on the dry Weight of the fiber can beused, though it is preferred as a factor of safety to employthree-fourths percent. Quantities up to 3 percent may be used ifnecessary to obtain the desired elfect. I In adidtion to employing themelamine-aldehyde condensation products, it has been found thaturea-aldehyde resins, such as Uforrnite 700, may be used with sub-.stantially equally effective results, though for ease of application andquality control, it is preferred to use the If emulsions are used it isadvisable to add suflicient alum to break the emulsion and precipitatethe material onto the fibers just as in case of sizing.

There are now available cationically active water-soluble or dispersibleaminoplastic resins which, by being substantive to cellulose, quicklyand completely become deposited upon the fibers of a pulp furnish.

In practice, the delamination-prevention agent is added to the furnishof the ply involved in the splitting. Figure 2, which is a greatlyenlarged fragment of a board core and contacting fibrous cover sheet,shows layers or plies contained in a manila cover sheet, though anyother type of cover sheet will serve for illustrative purposes. InFigure 2, ply 19 is shown as having split apart or delaminated, asdefined hereinabove, into a two section layer 19a and 1%. By adding themelamine-aldehyde resin to the furnish entering into the vat forming ply19 in suitable quantities, this ply 19 does not split or delaminate andthus gypsum wallboard can be produced without any rejects from thiscause.

Though it is obvious that the delarnination-prevention materials may bevaried somewhat in quantities and in action, nevertheless the importantfactor is that the delamination tendencies are entirely removed byadding to at least the ply adjacent the core, a resinous material havingthe property of increasing the wet-strength oi the paper of that ply. Itmay, with advantageous results, also be added to the other plies, but itappears that if it is present in the ply closest to the core, thedesired eifect is attained. It is therefore not intended to be limitedto the particular illustrated preferred embodiment, but only by theappended claims which define the fundamental concepts underlying thisinvention.

I claim:

1. Plaster board having paper cover sheets of a multiple ply nature inwhich the ply directly adjacent the set plaster core of such boardcontains about one-half to 3% by weight, of a wet-strength impartingaminoplastic resin substantially uniformly distributed throughout saidply.

2. The plaster board of claim 1 in which the wetstrength imparting resinis melamine-formaldehyde.

3. The plaster board of claim 1 in which the wetstrength imparting resinis urea-formaldehyde.

4. Plaster board having paper cover sheets of a multiple ply nature,only the ply directly adjacent the set plaster core of such boardcontaining about /2% to 3% by weight, of a wet-strength impartingaminoplastic resin substantially uniformly distributed throughout saidply.

5. Process of making a paper-covered plaster board which isresistant tointra-ply splitting which comprises forming a multi-ply paper-coversheet therefor by the steps of incorporating with the'fibers of the pulpforming the lowermost ply of said sheet prior to the formation of saidply from about one-half to three percent by Weight of awet-strenght-imparting aminoplastic resin, then imposing the other pliesthereto to form said sheet,

and using said sheet with said resin-containing layer in contact withthe plaster core of said board to form said board.

6. The process as claimed in claim 5, in which the resin is amelamine-formaldehyde resin.

. 7. The process as claimed in claim 5, in which the resin is aurea-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTSHuntzicker et al Mar. 18, 1952

5. PROCESS OF MAKING A PAPER-COVERED PLASTER BOARD WHICH IS RESISTANT TOINTRA-PLY SPLITTING WHICH COMPRISES FORMING A MULTI-PLY PAPER-COVERSHEET THEREFOR BY THE STEPS OF INCORPORATING WITH THE FIBERS OF THE PLUPFORMING THE LOWERMOST PLY OF SAID SHEET PRIOR TO THE FORMATION OF SAIDPLY FROM ABOUT ONE-HALF TO THREE PERCENT BY WEIGHT OF A WET-STTRENGHT-IMPARTING AMINOPLASTIC RESIN, THEN IMPOSING THE OTHER PLIES THERETO TOFORM SAID SHEET, AND USING SAID SHEET WITH SAID RESIN-CONTAINING LAYERIN CONTACT WITH THE PLASTER CORE OF SAID BOARD TO FORM SAID BOARD.